Magnetic resonance imaging method with hybrid filling of k-space
Abstract
A method for generating an image data set of an image area located in a measurement volume of a magnetic resonance system comprising a gradient system and an RF transmission/reception system, comprises the following method steps: —reading out k-space corresponding to the imaging area, by: (a) activating a frequency encoding gradient in a predetermined spatial direction and with a predetermined strength G0 by means of said gradient system, (b) after the activated frequency encoding gradient achieves its strength G0, radiating a non-slice-selective RF excitation pulse by means of said RF transmission/reception system, (c) after a transmit-receive switch time ΔtTR following the radiated excitation pulse, acquiring FID signals with said RF transmission/reception system and storing said FID signals as raw data points in k-space along a radial k-space trajectory that is predetermined by the direction and strength G0 of the frequency encoding gradient, (d) repeating (a) through (c) with respectively different frequency encoding gradient directions in each repetition until k-space corresponding to the image area is read out in an outer region of k-space along radial k-space trajectories, said radial k-space trajectories each having a radially innermost limit kgap which depends on said switch time ΔtTR, (e) reading out a remainder of k-space that corresponds to the imaging area, said remainder being an inner region of k-space not being filled by said first region and including at least a center of k-space, in a read out procedure that is different from (a) through (d), and storing all data points read out in (d) and (e); and —reconstructing image data from the read out data points in k-space by implementing a reconstruction algorithm; In order to constrain image fidelity and optimize scan duration under given circumstances, the inner k-space region is subdivided into a core region and at least one radially adjacent shell region.
Claims
exact text as granted — not AI-modifiedThe invention claimed is:
1. A method for generating an image data set of an image area located in a measurement volume of a magnetic resonance system, the magnetic resonance system comprising a gradient system and an RF transmission/reception system,
the method comprising:
reading out k-space corresponding to the imaging area, by:
(a) activating a frequency encoding gradient in a predetermined spatial direction and with a predetermined strength G 0 via said gradient system,
(b) after the activated frequency encoding gradient achieves its strength G 0 , radiating a non-slice-selective RF excitation pulse via said RF transmission/reception system,
(c) after a transmit-receive switch time Δt TR following the radiated excitation pulse, acquiring FID signals with said RF transmission/reception system and storing said FID signals as raw data points in k-space along a radial k-space trajectory that is predetermined by the direction and strength G 0 of the frequency encoding gradient,
(d) repeating (a) through (c) with respectively different frequency encoding gradient directions in each repetition until k-space corresponding to the image area is read out in an outer region of k-space along radial k-space trajectories, said radial k-space trajectories each having a radially innermost limit k gap which depends on said switch time Δt TR ,
(e) reading out a remainder of k-space that corresponds to the imaging area, said remainder being an inner region of k-space not being filled by said first region and including at least a center of k-space, in a read out procedure that is different from (a) through (d), and storing all data points read out in (d) and (e); and
reconstructing image data from the read out data points in k-space by implementing a reconstruction algorithm;
wherein
the inner k-space region is subdivided into a core region and at least one radially adjacent shell region with raw data points in the core region being acquired as Cartesian raw data, and raw data points in the shell region (S) being acquired along radial k-space trajectories using a gradient strength G that is smaller than the gradient strength G 0 .
2. The method according to claim 1 , wherein the boundary k gap subdividing the inner and outer k-space regions is given by the product of bandwidth BW and dead time Δt 0 , wherein the dead time Δt 0 is given by Δt RF , which is a part of the RF pulse plus the transmit-receive switch time Δt TR .
3. The method according to claim 1 , wherein the core region has an outer limit k core given by:
k
c
o
r
e
=
Δ
t
0
Δ
t
·
s
m
i
n
wherein
the dead time Δt 0 is given by Δt RF , which is a part of the RF pulse plus the transmit-receive switch time Δt TR ,
the allowed acquisition duration Δt is given by −T 2 ln(1−A) wherein A is an amplitude parameter selected between 0 and 1,
the minimum shell thickness s Min is selected to be between 0.1 and 10.
4. The method according to claim 1 , wherein the shell region comprises at least two shell regions (S 1 , S 2 , . . . ), each shell region S i having a shell thickness s i
given by
s
i
=
Δ
t
Δ
t
0
·
k
i
n
wherein
dead time Δt 0 is given by Δt RF , which is a part of an RF pulse plus the transmit-receive switch time Δt TR , and
allowed acquisition duration Δt is given by −T 2 ln(1−A) wherein A is an amplitude parameter selected between 0 and 1,
each shell region having an inner radius k in defined by the thickness of the next radially inward core or shell region.
5. The method according to claim 1 , wherein the reconstruction algorithm comprises a Fourier transformation of the data points.
6. The method according to claim 2 , wherein Δt RF is half of the RF pulse for symmetric RF pulses.
7. The method according to claim 3 , wherein Δt RF is half of the RF pulse for symmetric RF pulses.
8. The method according to claim 3 , wherein the minimum shell thickness s Min is between 0.5 and 2.
9. The method according to claim 3 , wherein the minimum shell thickness s Min is about 1.
10. The method according to claim 2 , wherein the shell region comprises at least two shell regions (S 1 , S 2 , . . . ), each shell region S, having a shell thickness s i
given by
s
i
=
Δ
t
Δ
t
0
·
k
i
n
wherein allowed acquisition duration Δt is given by −T 2 ln(1−A), wherein A is an amplitude parameter selected between 0 and 1,
each shell region having an inner radius k in defined by the thickness of the next radially inward core or shell region.
11. The method according to claim 3 , wherein the shell region comprises at least two shell regions (S 1 , S 2 , . . . ), each shell region S, having a shell thickness s i
given by
s
i
=
Δ
t
Δ
t
0
·
k
i
n
each shell region having an inner radius k in defined by the thickness of the next radially inward core or shell region.
12. The method according to claim 2 , wherein the reconstruction algorithm comprises a Fourier transformation of the data points.
13. The method according to claim 3 , wherein the reconstruction algorithm comprises a Fourier transformation of the data points.
14. The method according to claim 4 , wherein the reconstruction algorithm comprises a Fourier transformation of the data points.Cited by (0)
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